Balance step-height selective bi-channel structure on hkmg devices

ABSTRACT

The present disclosure provides a method including forming STI features in a silicon substrate, defining a first and a second active regions for a PFET and an NFET, respectively; forming a hard mask having an opening to expose the silicon substrate within the first active region; etching the silicon substrate through the opening to form a recess within the first active region; growing a SiGe layer in the recess such that a top surface of the SiGe layer within the first active region and a top surface of the silicon substrate within the second active region are substantially coplanar; forming metal gate material layers; patterning the metal gate material layers to form a metal gate stack on the SiGe layer within the first active region; and forming an eSiGe S/D stressor distributed in both the SiGe layer and the silicon substrate within the first active region.

PRIORITY DATA

This application claims priority to Provisional Application Ser. No.61/110,872 filed on Nov. 3, 2008, entitled “A Balance Step-HeightSelective Bi-Channel Structure on HKMG Devices,” the entire disclosureof which is incorporated herein by reference.

BACKGROUND

When a semiconductor device such as a field-effect transistor (FET) isscaled down through various technology nodes, high k dielectricmaterials and metals are adopted to form a gate stack. However, the highk and metal gate stack suffers from the high threshold voltage for ap-type FET. Therefore, a semiconductor device and a method of making thesame are needed to address the above issue.

SUMMARY

One of the broader forms of an embodiment of the present inventioninvolves a method for making a semiconductor device having metal gatestacks. The method includes forming shallow trench isolation (STI)features in a silicon substrate, defining a first active regionconfigured for a p-type field effect transistor (PFET) and a secondactive region configured for an n-type field effect transistor (NFET);forming, on the silicon substrate, a hard mask having an opening toexpose the silicon substrate within the first active region; etching thesilicon substrate through the opening of the hard mask to form a recessin the silicon substrate within the first active region; growing asilicon germanium (SiGe) layer in the recess such that a top surface ofthe SiGe layer within the first active region and a top surface of thesilicon substrate within the second active region are substantiallycoplanar; forming metal gate material layers on the silicon substrateand the SiGe layer; patterning the metal gate material layers to form ametal gate stack on the SiGe layer within the first active region; andforming an eSiGe source/drain (S/D) stressor distributed in both theSiGe layer and the silicon substrate within the first active region.

Another one of the broader forms of an embodiment of the presentinvention involves a method for making a semiconductor device havingmetal gate stacks. The method includes forming shallow trench isolation(STI) features in a silicon substrate, defining a first active regionconfigured for a first p-type field effect transistor (PFET), a secondactive region configured for an n-type field effect transistor (NFET),and a third active region configured for a second PFET, wherein thethird active region has a first dimension less than a second dimensionof the first active region; forming, on the silicon substrate, a hardmask having an opening that exposes the silicon substrate within thefirst active region; etching the silicon substrate through the openingof the hard mask to form a recess in the silicon substrate within thefirst active region; growing a silicon germanium (SiGe) layer in therecess such that a top surface of the SiGe layer within the first activeregion and a top surface of the silicon substrate within the second andthird active regions are substantially coplanar; forming metal gatematerial layers on the silicon substrate and the SiGe layer; patterningthe metal gate material layers to form a first metal gate stack on theSiGe layer within the first active region and a second metal gate stackon the silicon substrate within the third active region; and formingfirst source/drain (S/D) features distributed in both the SiGe layer andthe silicon substrate within the first active region and second S/Dfeatures distributed in the silicon substrate within the third activeregion.

Yet another one of the broader forms of an embodiment of the presentinvention involves a semiconductor device. The semiconductor deviceincludes a silicon substrate having a first active region and a secondactive region; a silicon germanium (SiGe) feature on the siliconsubstrate within the first active region, the SiGe feature within thefirst active region and the silicon substrate within the second activeregion are substantially coplanar; a p-type field effect transistor(PFET) formed in the first active region including: first source/drain(S/D) features distributed in the SiGe feature and the siliconsubstrate; a first channel in the SiGe layer, disposed between the firstS/D features; and a first metal gate stack disposed on the SiGe layerand overlying the first channel; and an n-type field effect transistor(NFET) formed in the second active region including: second source/drain(S/D) features distributed in the silicon substrate; a second channel inthe silicon substrate, disposed between the second S/D features; and asecond metal gate stack disposed on the silicon substrate, overlying thesecond channel, and being different from the first metal gate stack incomposition.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion. Particularly,

FIG. 1 is a flowchart of a method for making a semiconductor devicehaving a metal gate structure constructed according to aspects of thepresent disclosure.

FIGS. 2 through 11 are sectional views of a semiconductor device atvarious fabrication stages in one or more embodiments of the method ofFIG. 1.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a first feature over or on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

FIG. 1 is a flowchart of a method 100 for making a semiconductor devicehaving a metal gate structure constructed according to aspects of thepresent disclosure. FIGS. 2 through 11 are sectional views of asemiconductor device 200 having a metal gate structure constructedaccording to aspects of the present disclosure in various embodiments.The semiconductor device 200 and the method 100 of making the same arecollectively described below.

Referring to FIGS. 1 and 2, the method 100 begins at step 102 by formingshallow trench isolation (STI) features 212 in a semiconductor substrate210. The semiconductor substrate 210 includes silicon. The substratefurther includes various doped features, such as n type wells and p typewells formed by various ion implantation or diffusion techniques knownin the art. The STI features define various active regions. In oneembodiment, the substrate includes a first active region 216 configuredfor a p-type field-effect transistor (PFET) and a second active region214 configured for an n-type field-effect transistor (PFET). In anotherembodiment, the substrate 210 additionally includes a third activeregion 218 configured for a second PFET. The first active region 216 hasa dimension L1 greater than a dimension L2 of the third active region218, as illustrated in FIG. 2. In one example, L2 is about 50% of L1 orless. The STI features 212 can be formed by etching the substrate toform trenches and filling the trenches with one or more dielectricmaterials. A chemical mechanical polishing (CMP) process may followthereafter to remove the excess dielectric materials and reduce thesurface variation of the substrate. In one example, the STI features 212include silicon oxide. The silicon oxide can be filled in the trenchesby a chemical vapor deposition (CVD) process. In various examples, thesilicon oxide can be formed by a high density plasma chemical vapordeposition (HDPCVD). In another embodiment, the trench isolationfeatures may include a multi-layer structure. In furtherance of theembodiment, the trench isolation features include other suitablematerials, such as silicon nitride, silicon oxynitride, low k materials,air gap, or combinations thereof. For example, the trench isolationfeatures 218 include a thermal oxide lining layer to improve the trenchinterface.

Referring to FIGS. 1 and 3, the method 100 proceeds to step 104 byforming a hard mask 220 patterned to having one or more openings toexpose the silicon substrate within the first active region 216. Thehard mask 220 may include silicon nitride or other suitable material,such as silicon oxynitride. In another example, the hard mask includesone or more dielectric materials and is formed by a suitable process,such as CVD. In various embodiments, the hard mask layer includessilicon oxide, silicon nitride, silicon oxynitride or a combinationthereof in a multi-film structure. In one example, the hard mask 220 hasa thickness of about 3 nm. The hard mask 220 can be formed by aprocedure including deposition, lithography process and etching. Forexample, forming a hard mask layer on the substrate and then forming apatterned resist layer 222 on the hard mask layer. The patterned resistlayer is formed by a photolithography process. An exemplaryphotolithography process may include processing steps of photoresistcoating, soft baking, mask aligning, exposing, post-exposure baking,developing photoresist and hard baking. The photolithography exposingprocess may also be implemented or replaced by other proper methods suchas maskless photolithography, electron-beam writing, ion-beam writing,and molecular imprint. The etching can be a dry etching process toremove the hard mask layer within the opening of the patterned resistlayer in one example. In one embodiment, the second and third activeregions are covered by the hard mask. The patterned resist layer isremoved thereafter by a process, such as a wet stripping or plasmaashing.

Referring to FIGS. 1 and 4, the method 100 proceeds to step 106 byetching the silicon substrate within the first active region through theopening of hard mask, such that the silicon substrate within the firstactive region is recessed. In one embodiment, the silicon recess has adepth of about 10 nm. The etching process may include plasma etchingutilizing a suitable etchant, such as flurine (F)-containing gas. Invarious examples, the etchant includes CF4, SF6, NF3, or combinationsthereof.

Still referring to FIGS. 1 and 4, the method 100 proceeds to step 108 bygrowing silicon germanium (SiGe) in the recessed silicon substratewithin the first active region by a selective epi growth (SEG) or othersuitable epi. technology. The epi grown SiGe layer 224 fills in thesilicon recess such that the top surface of the SiGe layer within thefirst active region and the top surface of the silicon substrate withinthe second active region are substantially coplanar. In one embodiment,the SiGe layer 224 has a thickness of about 10 nm. In anotherembodiment, a thin silicon 236 is additionally formed on the SiGe layer224 by epi growth, as illustrated in FIG. 10. Then an oxidizationprocess is applied to the thin silicon layer 236 to transfer the thinsilicon layer into a silicon oxide layer 238 as illustrated in FIG. 11.For example, an oxygen gas and a high temperature are applied to thethin silicon layer 236 to form the silicon oxide layer 238. In oneexample, such a silicon oxide layer may be formed on the SiGe layer 224for a low-speed PFET.

Referring to FIGS. 1 and 5, the method 100 proceeds to step 110 byremoving the hard mask. The hard mask layer 220 can be removed by anetching process, such as a wet etch. In one embodiment, a hot phosphoricacid (H3PO4) is used as an ethcant to remove the hard mask of siliconnitride.

Referring to FIGS. 1 and 6, the method 100 proceeds to step 112 byforming various metal gate material layers 226 on the silicon substrateand the SiGe layer, using various deposition technique such as CVD,atomic layer deposition (ALD) or physical vapor deposition (PVD). Themetal gate material layers include a high k dielectric material layer.The high k dielectric material layer is formed by a suitable processsuch as ALD. Other methods to form the high k dielectric material layerinclude metal organic chemical vapor deposition (MOCVD), physical vapordeposition (PVD), UV-Ozone Oxidation and molecular beam epitaxy (MBE).In one embodiment, the high k dielectric material includes hafnium oxide(HfO). Alternatively, the high k dielectric material layer includesmetal nitrides, metal silicates or other metal oxides.

An interfacial layer (IL) may be additionally formed on the substrateand is interposed between the SiGe layer and the high k dielectricmaterial layer. The interfacial layer includes a thin silicon oxidelayer in one example. In one embodiment, the thin silicon oxide can beformed by the method illustrated in FIGS. 10 and 11. In anotherembodiment, the thin silicon oxide can be formed by ALD.

The metal gate material layers includes a metal layer formed on the highk dielectric material layer. The metal layer is formed by PVD or othersuitable process. In one embodiment, the metal layer includes titaniumnitride. In another embodiment, the metal gate layer may includetantalum nitride, molybdenum nitride, tungsten nitride, tungsten,tantalum carbide, tantalum carbide nitride, titanium aluminum nitride ora combination thereof. The metal layer is chosen to have a proper workfunction for p-type field effect transistor or mid gap work function forboth p-type and n-type transistors. In one embodiment, the metal layerhas a thickness less than about 50 angstrom. In another embodiment, themetal layer may have a multi-film structure designed to have a properwork function.

The metal gate material layers may include a capping layer interposedbetween the high k dielectric material layer and the metal layer. In oneembodiment, the capping layer includes lanthanum oxide (LaO). Thecapping layer may alternatively includes other suitable material, suchas aluminum oxide (Al2O3). The capping layer can be formed by a suitableprocess, such as PVD or ALD.

The metal gate material layers further includes a conductive materiallayer disposed on the metal layer. In one embodiment, the conductivematerial layer includes doped polysilicon. The polysilicon layer may beformed by a chemical vapor deposition (CVD) process. Silane (SiH4) canbe employed a chemical gas in the CVD process to form the silicon layer.In one embodiment, the silicon layer has a thickness less than about 700angstrom. In another embodiment, the conductive material layeralternatively includes other suitable material, such as copper,aluminum, tungsten, or metal silicide.

Referring to FIGS. 1 and 7, the method 100 proceeds to step 114 bypatterning the various gate material layers to form one or more metalgate stacks 228. For example, a first metal gate stack within the firstactive region, a second metal gate stack is formed within the secondactive region and a third metal gate stack is formed within the thirdactive region. The metal gate stacks are formed by an etching procedureusing an etch mask.

In one embodiment, the etch mask uses a hard mask of an etch-selectivematerial. In this case, a hard mask layer formed on the conductivematerial layer. The hard mask layer includes one or more dielectricmaterials and is formed by a suitable process, such as CVD. In variousembodiments, the hard mask layer includes silicon oxide, siliconnitride, silicon oxynitride or a combination thereof in a multi-filmstructure. A patterned resist layer is formed on the hard mask layer.Then the hard mask layer is etched away within the openings of thepatterned resist layer, resulting in a patterned hard mask. The etchingprocess applied to the hard mask layer can be a wet etching process or adry etching process. For example, a hydrofluoric (HF) solution may beused to etch a silicon oxide hard mask layer. The patterned resist layeris formed by a photolithography process.

In another embodiment, the hard mask layer may be avoid. In this case,the etch mask can be a patterned resist layer formed on the metal gatematerial layers, defining one or more openings of the resist layer. Themetal gate layers are patterned by directly forming the patterned resistlayer on the conductive material layer and then etching the metal gatematerial layers through the openings of the patterned resist layer.

The etching procedure involves one or more wet or dry etchings toeffectively remove the various metal gate material layers within theopenings of the etch mask. In one embodiment, the etching procedureutilizes a dry etching process. In one example, the dry etching processimplements a fluorine-containing plasma to remove the silicon layer. Inanother example, the dry etching process with the fluorine-containingplasma is implemented to remove the polysilicon layer, the metal layerand the high k dielectric material layer. Alternatively, the etchingprocess may include multiple etching steps to etch the various gatematerial layers.

Referring to FIGS. 1 and 8, the method 100 may proceed to step 116 byperforming various ion implantations. In one embodiment, a dielectriclayer 230 is formed on the sidewalls of the metal gate stacks 228. Thedielectric layer 230 is disposed on the sidewalls of the metal gatestack such that the subsequent ion implantation are offset from themetal gate stack for better device performance. Additionally oralternatively, the dielectric layer can function to seal the high kdielectric material layer and the metal layer, therefore protectingthese gate materials. The dielectric layer 230 includes silicon oxide,silicon nitride or other suitable dielectric material. The dielectriclayer 230 can be formed by CVD, PVD or other suitable process.

Still referring to FIG. 8, various ion implantations are performed tothe silicon substrate 210 and/or the SiGe layer 224. In one embodiment,a light doped drain (LDD) regions are formed by an ion implantationprocess using the gate stack as an implanting mask. The LDD regions aresubstantially aligned with the edges of the gate stack. If thedielectric layer is present, the LDD regions are offset from the edge ofthe gate stack by the dielectric layer. Additionally, a halo/pocketimplantation process may be implemented to eliminate the short channeleffect.

Particularly, an epi silicon germanium source/drain (eSiGe S/D) stressor234 are formed in the first active region by an ion implantation. TheeSiGe S/D stressor 234 is configured in the first active region for thestrain effect to enhance the mobility in the channel region. The eSiGeS/D stressor 234 is a doped feature vertically distributed in both theSiGe layer and the silicon substrate. In one embodiment, the eSiGe S/Dstressor is an additional doped feature with implanted ions, such assilicon, germanium, boron, gallium or combinations thereof. In anotherembodiment, the eSiGe S/D stressor may include the LDD and/or the halodoped features in the first active region.

Referring to FIGS. 1 and 9, the method 100 may proceed to step 118 byforming a spacer 232. The spacer 232 is formed on the sidewalls of thegate stack (or the sidewalls of the dielectric layer if present) by atechnique known in the art. For example, the spacer includes siliconnitride and is formed by a chemical vapor deposition (CVD) and then adry etching process. The spacer 232 may have a multiple-layer structure.

Still referring to FIGS. 1 and 9, the method 100 may proceed to step 120by forming source and drain features using another ion implantationprocess. Thus formed source and drain are further offset from the gatestack by the spacer 232. An annealing process may be applied thereafterto the substrate to activate the source/drain features and/or otherdoped features performed at step 116. The annealing process can beimplemented by a suitable method, such as rapid thermal annealing orlaser annealing. In another embodiment, the eSiGe S/D stressor 234includes S/D features.

Thus formed semiconductor device 200 includes a PFET that has the SiGelayer coplanar with the silicon substrate within the second activeregion. Additionally, the PFET has a channel defined in the SiGe layerwith enhanced mobility. The PFET further includes the eSiGe stressorformed in the first active region and distributed vertically in both theSiGe layer and the silicon substrate underlying the SiGe layer. Thethreshold voltage of the PFET can be reduced by the disclosed structure.

Although not shown, other processing step may present to form variousdevices features such as multilayer interconnection (MLI) and interlayerdielectric (ILD). In one embodiment, the multilayer interconnection arefurther formed. The multilayer interconnection includes verticalinterconnects, such as conventional vias or contacts, and horizontalinterconnects, such as metal lines. The various interconnection featuresmay implement various conductive materials including copper, tungstenand silicide. In one example, a damascene process is used to form copperrelated multilayer interconnection structure. In another embodiment,tungsten is used to form tungsten plug in the contact holes.

Other processing steps may follow to form other features of thesemiconductor device 200 after the method 100. For example, an ILD layeris formed on the substrate and the gate stacks, then a CMP process isapplied to the substrate, and then the contacts to the source/drain andthe gates are formed in the ILD.

The present disclosure is not limited to applications in which thesemiconductor structure includes a MOS transistor, and may be extendedto other integrated circuit having a dynamic random access memory (DRAM)cell, a single electron transistor (SET), and/or other microelectronicdevices (collectively referred to herein as microelectronic devices). Inanother embodiment, the semiconductor device 200 includes FinFETtransistors. Of course, aspects of the present disclosure are alsoapplicable and/or readily adaptable to other type of transistor, suchmultiple-gate transistors, and may be employed in many differentapplications, including sensor cells, memory cells, logic cells, andothers.

Although embodiments of the present disclosure have been described indetail, those skilled in the art should understand that they may makevarious changes, substitutions and alterations herein without departingfrom the spirit and scope of the present disclosure. In anotherembodiment, the SiGe layer may be additionally formed in the PFET withinthe small active region, such as the third active region 218. In anotherembodiment, a silicon carbide (SIC) epi layer is formed similar in thesecond active region for the NFET such that the NFET channel is formedin the SiC layer and the mobility of the BFET channel is enhanced. Inanother embodiment, the metal gate stack for the NFET in the secondactive region is different from the metal gate stack for the PFET in thefirst active region in term of composition. For example, the metal layerin the metal gate stack of the NFET uses different metal material suchthat the work function can be properly tuned for the PFET. In anotherembodiment, the substrate may include a semiconductor-on-insulator (SOI)structure such as a buried dielectric layer.

In another embodiment, the various gate stacks may be formed by a hybridapproach wherein one type of stacks are formed by a gate-first approachand the another type gate stacks are formed by a gate-last approach. Inanother embodiment, the NFET is formed by a gate-last process.

Thus, the present disclosure provides a method for making an integratedcircuit having metal gate stacks. The method includes forming shallowtrench isolation (STI) features in a silicon substrate, defining a firstactive region configured for a p-type field effect transistor (PFET) anda second active region configured for an n-type field effect transistor(NFET); forming, on the silicon substrate, a hard mask designed havingan opening to expose the silicon substrate within the first activeregion; etching the silicon substrate through the opening of the hardmask to form a recess in the silicon substrate within the first activeregion; growing a silicon germanium (SiGe) layer on the siliconsubstrate within the first active region such that a top surface of theSiGe layer within the first active region and a top surface of thesilicon substrate within the second active region are substantiallycoplanar; forming metal gate material layers on the silicon substrateand the SiGe layer; patterning the metal gate material layers to form ametal gate stack on the SiGe layer within the first active region; andforming an eSiGe source/drain stressor distributed in both the SiGelayer and the silicon substrate within the first active region.

In various embodiments, the disclosed method further includes forming afirst dielectric layer on the metal gate stack; forming light-dopeddrain (LDD) features in the SiGe layer; and forming a spacer on sidewallof the first dielectric layer before forming of the eSiGe S/D stressor.The method further include applying at least one of pocket and haloimplantations to the SiGe layer within the first active region beforethe forming of the spacer. The forming of the metal gate material layersincludes forming a high k dielectric layer; forming a metal layer on thehigh k dielectric layer; and forming a conductive layer on the metallayer. The conductive layer may include doped polysilicon. The methodmay further include forming a thin silicon layer on the SiGe layer byepi growth; and implementing an oxidization process to the thin siliconlayer to transfer the thereof into a silicon oxide layer before theforming of the metal gate material layers. The method may furtherinclude removing the hard mask after the growing the SiGe layer.

The present disclosure also provide a method for making a semiconductordevice having metal gate stacks in another embodiment. The methodincludes forming shallow trench isolation (STI) features in a siliconsubstrate, defining a first active region configured for a p-type fieldeffect transistor (PFET), a second active region configured for ann-type field effect transistor (NFET), and a third active regionconfigured for a second PFET, wherein the third active region has afirst dimension less than a second dimension of the first active region;forming, on the silicon substrate, a hard mask patterned to have anopening to expose the silicon substrate within the first active region;etching the silicon substrate through the opening of the hard mask toform a recess in the silicon substrate within the first active region;growing a silicon germanium (SiGe) layer on the silicon substrate withinthe first active region such that a top surface of the SiGe layer withinthe first active region and a top surface of the silicon substratewithin the second and third active regions are substantially coplanar;forming metal gate material layers on the silicon substrate and the SiGelayer; patterning the metal gate material layers to form a first metalgate stack on the SiGe layer within the first active region and a secondmetal gate stack on the silicon substrate within the third activeregion; and forming first source/drain (S/D) features distributed inboth the SiGe layer and the silicon substrate within the first activeregion and second S/D features distributed in the silicon substratewithin the third active region.

The method may further include forming a first dielectric layer on themetal gate stack; thereafter forming light-doped drain (LDD) features inthe SiGe layer; and forming a spacer on sidewall of the first dielectriclayer before forming of the first and second S/D features. The methodmay further include applying a halo ion implantation to the SiGe layerwithin the first active region before the forming of the spacer. Theforming of the metal gate material layers may include forming a high kdielectric layer; forming a capping layer on the high k dielectriclayer; forming a metal layer on the high k dielectric layer; and forminga conductive layer on the metal layer. The method may further includeforming a second hard mask on the silicon substrate patterned to have anopening exposing the silicon substrate within the second active region;etching the silicon substrate within the second active region throughthe opening of second hard mask; and growing a silicon carbide (SiC)layer on the silicon substrate within the second active region such thatthe SiC layer and the SiGe layer are substantially coplanar. The methodmay further include removing the second hard mask after the growing ofthe SiC layer. The method of may further include forming second metalgate layers on the SiC layer, the second metal gate layers are differentfrom the metal gate layers in composition; and patterning the secondmetal gate layers to form a second metal gate stack on the SiC layerwithin the second active region.

The present disclosure also provides a semiconductor device including asilicon substrate having a first active region and a second activeregion; a silicon germanium (SiGe) feature on the silicon substratewithin the first active region, the SiGe feature within the first activeregion and the silicon substrate within the second active region aresubstantially coplanar; a p-type field effect transistor (PFET) formedin the first active region; and an n-type field effect transistor (NFET)formed in the second active region. The PFET includes first source/drain(S/D) features distributed in the SiGe feature and the siliconsubstrate; a first channel in the SiGe layer, disposed between the firstS/D features; and a first metal gate stack disposed on the SiGe layerand overlying the first channel. The NFET includes second source/drain(S/D) features distributed in the silicon substrate; a second channel inthe silicon substrate, disposed between the second S/D features; and asecond metal gate stack disposed on the silicon substrate, overlying thesecond channel, and being different from the first metal gate stack incomposition.

The device may further include a dielectric layer disposed on sidewallsof the first metal gate stack; and a spacer disposed on the dielectriclayer. The device may further include a second PFET formed in a thirdactive region, wherein the silicon substrate within the third activeregion has a top surface substantially coplanar to a top surface of theSiGe layer within the first active region, the third active region has afirst dimension less then a second dimension of the first active region.The second PFET includes third source/drain (S/D) features distributedin the SiGe feature and the silicon substrate; a third channel in thesilicon substrate, disposed between the third S/D features; and a thirdmetal gate stack disposed on the silicon substrate layer and overlyingthe third channel, the third metal gate stack being substantiallysimilar to the first metal gate stack in composition. The first andthird metal gate stack may include a silicon oxide layer; a high kdielectric material layer on the silicon oxide layer; a first metallayer on the high k dielectric material layer; and a conductive layer onthe first metal layer. The second metal gate stack may include thesilicon oxide layer; the high k dielectric material layer on the siliconoxide layer; a second metal layer on the high k dielectric materiallayer, the second metal layer being different from the first metal layerin composition; and the conductive layer on the second metal layer.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

1. A method for making a semiconductor device having metal gate stackscomprising: forming shallow trench isolation (STI) features in a siliconsubstrate, defining a first active region configured for a p-type fieldeffect transistor (PFET) and a second active region configured for ann-type field effect transistor (NFET); forming, on the siliconsubstrate, a hard mask having an opening to expose the silicon substratewithin the first active region; etching the silicon substrate throughthe opening of the hard mask to form a recess in the silicon substratewithin the first active region; growing a silicon germanium (SiGe) layerin the recess such that a top surface of the SiGe layer within the firstactive region and a top surface of the silicon substrate within thesecond active region are substantially coplanar; forming metal gatematerial layers on the silicon substrate and the SiGe layer; patterningthe metal gate material layers to form a metal gate stack on the SiGelayer within the first active region; and forming an eSiGe source/drain(S/D) stressor distributed in both the SiGe layer and the siliconsubstrate within the first active region.
 2. The method of claim 1,further comprising: forming a first dielectric layer on the metal gatestack; forming light-doped drain (LDD) features in the SiGe layer; andforming a spacer on sidewall of the first dielectric layer prior toforming of the eSiGe S/D stressor.
 3. The method of claim 2, furthercomprising applying at least one of a pocket implantation and a haloimplantation to the SiGe layer within the first active region prior toforming of the spacer.
 4. The method of claim 1, wherein the forming ofthe metal gate material layers comprises: forming a high k dielectriclayer; forming a metal layer on the high k dielectric layer; and forminga conductive layer on the metal layer.
 5. The method of claim 4, whereinthe conductive layer comprises doped polysilicon.
 6. The method of claim1, further comprising: forming a thin silicon layer on the SiGe layer byepi growth; and implementing an oxidization process to transform thethin silicon layer into a silicon oxide layer prior to forming of themetal gate material layers.
 7. The method of claim 1, further comprisingremoving the hard mask after growing the SiGe layer.
 8. A method formaking a semiconductor device having metal gate stacks comprising:forming shallow trench isolation (STI) features in a silicon substrate,defining a first active region configured for a first p-type fieldeffect transistor (PFET), a second active region configured for ann-type field effect transistor (NFET), and a third active regionconfigured for a second PFET, wherein the third active region has afirst dimension less than a second dimension of the first active region;forming, on the silicon substrate, a hard mask having an opening thatexposes the silicon substrate within the first active region; etchingthe silicon substrate through the opening of the hard mask to form arecess in the silicon substrate within the first active region; growinga silicon germanium (SiGe) layer in the recess such that a top surfaceof the SiGe layer within the first active region and a top surface ofthe silicon substrate within the second and third active regions aresubstantially coplanar; forming metal gate material layers on thesilicon substrate and the SiGe layer; patterning the metal gate materiallayers to form a first metal gate stack on the SiGe layer within thefirst active region and a second metal gate stack on the siliconsubstrate within the third active region; and forming first source/drain(S/D) features distributed in both the SiGe layer and the siliconsubstrate within the first active region and second S/D featuresdistributed in the silicon substrate within the third active region. 9.The method of claim 8, further comprising forming a first dielectriclayer on the first metal gate stack; thereafter forming light-dopeddrain (LDD) features in the SiGe layer; and forming a spacer on sidewallof the first dielectric layer prior to forming of the first and secondS/D features.
 10. The method of claim 8, further comprising applying ahalo ion implantation to the SiGe layer within the first active regionprior to forming of the spacer.
 11. The method of claim 8, wherein theforming of the metal gate material layers comprising: forming a high kdielectric layer; forming a capping layer on the high k dielectriclayer; forming a metal layer on the high k dielectric layer; and forminga conductive layer on the metal layer.
 12. The method of claim 8,further comprising: forming a second hard mask on the silicon substratepatterned to have an opening exposing the silicon substrate within thesecond active region; etching the silicon substrate within the secondactive region through the opening of second hard mask to form a secondrecess in the silicon substrate within the second active region; andgrowing a silicon carbide (SiC) layer in the second recess such that theSiC layer and the SiGe layer are substantially coplanar.
 14. The methodof claim 13, further comprising removing the second hard mask after thegrowing of the SiC layer.
 15. The method of claim 13, furthercomprising: forming second metal gate layers on the SiC layer, thesecond metal gate layers are different from the metal gate layers incomposition; and patterning the second metal gate layers to form asecond metal gate stack on the SiC layer within the second activeregion.
 16. A semiconductor device, comprising: a silicon substratehaving a first active region and a second active region; a silicongermanium (SiGe) feature on the silicon substrate within the firstactive region, the SiGe feature within the first active region and thesilicon substrate within the second active region are substantiallycoplanar; a p-type field effect transistor (PFET) formed in the firstactive region including: first source/drain (S/D) features distributedin the SiGe feature and the silicon substrate; a first channel in theSiGe layer, disposed between the first S/D features; and a first metalgate stack disposed on the SiGe layer and overlying the first channel;and an n-type field effect transistor (NFET) formed in the second activeregion including: second source/drain (S/D) features distributed in thesilicon substrate; a second channel in the silicon substrate, disposedbetween the second S/D features; and a second metal gate stack disposedon the silicon substrate, overlying the second channel, and beingdifferent from the first metal gate stack in composition.
 17. The deviceof claim 16, further comprising: a dielectric layer disposed onsidewalls of the first metal gate stack; and a spacer disposed on thedielectric layer.
 18. The device of claim 16, further comprising asecond PFET formed in a third active region, wherein the siliconsubstrate within the third active region has a top surface substantiallycoplanar to a top surface of the SiGe layer within the first activeregion, the third active region has a first dimension less then a seconddimension of the first active region, and the second PFET includes:third source/drain (S/D) features distributed in the SiGe feature andthe silicon substrate; a third channel in the silicon substrate,disposed between the third S/D features; and a third metal gate stackdisposed on the silicon substrate layer and overlying the third channel,the third metal gate stack being substantially similar to the firstmetal gate stack in composition.
 19. The device of claim 16, wherein thefirst and third metal gate stack comprise: a silicon oxide layer; a highk dielectric material layer on the silicon oxide layer; a first metallayer on the high k dielectric material layer; and a conductive layer onthe first metal layer.
 20. The device of claim 19, wherein the secondmetal gate stack comprises: the silicon oxide layer; the high kdielectric material layer on the silicon oxide layer; a second metallayer on the high k dielectric material layer, the second metal layerbeing different from the first metal layer in composition; and theconductive layer on the second metal layer.